In principle, hydrocarbons which are the main constituent of petroleum fuel should react with oxygen according to the theoretical chemical equation, EQU C.sub.m H.sub.n + (m + 4)O.sub.2 .fwdarw. mCO.sub.2 + n/2 H.sub.2 O
by combustion in an engine. However, in addition to the combustion based on the above equation other chemical reactions also occur within the engine of a car. Namely, large quantities of carbon monoxide (CO) and gaseous hydrocarbons formed by combustion of petroleum are produced and exhausted from the engine. Nitrogen monoxide (NO) is also produced by combustion at high compression within the engine of the car. This NO reacts with 0.sub.2 in the atmosphere to form NO.sub.x an addition product of nitrogen dioxide.
Presently, methods for treating exhaust gases from cars include controlling the circulation of gas, controlling the amount of air introduced into the engine, reducing combustion of gases and an afterburner using particle catalyst. Metal particle catalysts have been applied in most conventional methods using a catalyst. But particle catalysts have disadvantages in that the efficiency of oxidation, the most important feature, is limited and the life of the catalysts is short. Metal particle catalyst, consisting of platinum are high in cost. Furthermore, the particle catalysts are easily poisoned due to the surfaces of the catalysts being covered with carbon, lead or aromatic hydrocarbons such as benzene, toluene and xylene. Therefore, further research is required to use metal particle catalysts practically.
It is because of the present nature of an internal combustion car engine that poisonous exhaust gases are released into the atmosphere. The combustion chamber of the engine is made in a flat shape in order to obtain high h.p. As the surface area of the combustion chamber is large compared with its volume, quenching occurs. The amount of CO produced is not influenced by the ratio of the surface area of the combustion chamber to its volume (S/V), but the amount of gaseous hydrocarbons is affected by this ratio. It is difficult to make the ratio less than 7 in the case of small engines. Besides the shape of the combustion chamber, the ratio S/V is also determined by the compression ratio, the ratio of stroke/bore, the number of cylinders, and the cylinder capacity of the engine. An engine having a low compression ratio, a long stroke, and a smaller number of cylinders exhausts less poisonous gases than a conventional small engine having a high rotation and large h.p. Although the volume ratio S/V is small when the shape of the engine is spherical, this alone is not effective to decrease the amount of poisonous exhaust gases.